The present invention relates to medical diagnostic apparatus, and in particular, to brain-stem electric response audiometry.
Brain-stem electric response audiometry (BSER) is a clinical technique used for detection and diagnosis of tumors or other abnormalities in the portion of the brain related to the auditory function. In general, a stimulus comprising a pulse of acoustic energy (characterized by an abrupt onset and decay, and of short duration), is directed against the tympanic membrane of the ear, and the resultant electric activity of the brain is recorded and evaluated. Commonly, a pathologically involved ear and auditory neurological pathway manifests a greater time interval (referred to as the latency) between the application of the stimulus and the electrical response of the brain stem. Abnormalities in both the morphology (waveshape) and temporal characteristics of the recorded electrical wave patterns are diagnostically significant.
Comparison of the latencies of the respective ears (with stimuli amplitude levels corrected for any conductive hearing loss) is referred to as "differential latency" of the subject.
The patient's response to the BSER stimulus is a very low level electrical voltage, typically on the order of 250 nV and must be extracted from a relatively noisy environment. The subject's body can accumulate a significant alternating current voltage at the frequency of utility power, e.g., 60 Hz and its harmonics. In addition, electrical connections must be made at the surface of the skin, introducing a significant electrical resistance. Accordingly, current BSER instruments are highly sophisticated and expensive equipment. Such instruments typically include special preamplifier circuits and employ microprocessors to accumulate many thousands of BSER responses, which are processed to distinguish the BSER wave pattern from normal background electrical noise. Such current BSER techniques, in addition to requiring expensive equipment, are also cumbersome and time consuming.